In recent years, as part of response to the environment, removal of lead from semiconductor products has proceeded. In addition, since lead-free solder is used in installation on substrates, the solder reflow temperature is higher than in the case of conventional tin-lead solder. Therefore, as die-attach materials which adhere a semiconductor element such as an IC to a support such as a metal frame or an organic substrate, die-attach materials which can sufficiently withstand an increase in stress in a semiconductor package accompanying an increase in solder reflow temperature and on which peeling between members (for example, semiconductor element/sealing material, semiconductor element/die-attach layer, die-attach layer/solder resist (substrate surface), interior part of substrate (solder resist/copper trace), lead frame/die-attach layer, lead frame/sealing material, and the like) does not easily occur, that is, a die-attach material having a low-stress property and a high adhesion property at high temperature are particularly desirable.
Furthermore, recently, while a reduction in size and weight, a reduction in thickness, and an increase in functionality have proceeded remarkably in electronics such as cell phones, it is strongly required to reduce the sizes and thicknesses of semiconductor packages themselves, and with this, it is necessary to reduce the thickness of a semiconductor element in the semiconductor packages. As die-attach materials which adhere a semiconductor element to a support, a liquid die-attach material is often used due to reasons such as merits in terms of cost. However, when a liquid die-attach material is used in mounting of a semiconductor element which has been made thinner on a support, the liquid die-attach material easily creeps to an upper part of the semiconductor element, and thus it is desirable for the liquid die-attach material to exhibit favorable wet spreadability even under lower pressure in addition to the low-stress property and the high adhesion property at high temperature.
In order to meet requirements for the low-stress property and the high adhesion property at high temperature, a method in which a high-molecular-weight component having a low glass transition temperature (Tg) is added (for example, see Patent Document 1) has been considered. However, in this method, in order to obtain a liquid die-attach material, a large amount of diluent or solvent is used in order to dissolve the high-molecular-weight component and there is a problem in that the obtained die-attach material easily becomes stringy and thus has low coating applicability. When the die-attach material has a film shape, the influence on workability is removed. However, the film-shaped die-attach material is very poor in terms of embeddability into irregularities derived from the presence or absence of wirings on a surface of a support such as an organic substrate with a semiconductor element adhered thereto, and thus has a problem in that voids are easily caused.
In order to solve the problems, a method using a compound having a molecular weight of 1000 to 20000 has been considered and a liquid resin composition having excellent coating applicability and solder cracking resistance has been invented (for example, see Patent Document 2). However, when the compound having a molecular weight of 1000 to 20000 is added in such an amount as to exhibit favorable solder cracking resistance, the viscosity of the liquid resin composition increases and this causes a deterioration in wet spreadability under low pressure at the time of mounting a semiconductor element for which there has been highly demanded in recent years. As described above, there have been no liquid die-attach materials which can simultaneously satisfy the solder cracking resistance and the wet spreadability under low pressure at the time of mounting a semiconductor element.